feat: implement Blazor web interface for GM session management

- Created GmRelay.Web project (Blazor Server)
- Created GmRelay.Shared library for domain models and rendering
- Refactored GmRelay.Bot to use the Shared library
- Integrated Telegram Login widget with server-side HMAC verification
- Added Dashboard, Group Details, and Edit Session pages
- Enabled bot notifications and in-place message updates from web actions
- Updated .NET Aspire orchestration and Docker Compose configuration

src/GmRelay.Web/Components/Layout/MainLayout.razor

@@ -0,0 +1,23 @@
+@inherits LayoutComponentBase
+
+<div class="page">
+    <div class="sidebar">
+        <NavMenu />
+    </div>
+
+    <main>
+        <div class="top-row px-4">
+            <a href="https://learn.microsoft.com/aspnet/core/" target="_blank">About</a>
+        </div>
+
+        <article class="content px-4">
+            @Body
+        </article>
+    </main>
+</div>
+
+<div id="blazor-error-ui" data-nosnippet>
+    An unhandled error has occurred.
+    <a href="." class="reload">Reload</a>
+    <span class="dismiss">🗙</span>
+</div>